Thermoplastic adhesives or so-called "hot melt" adhesives are now widely used to secure substrates together in a great variety of applications. These hot melt materials are essentially solvent free adhesives which are applied in a molten state and form a bond upon cooling to a solid state. By reason of their quick setting characteristics, their adhesive "tack" and their gap filling properties, they are used in many industrial adhesive applications. For example, such adhesives are now commonly used in the assembly and manufacture of automobiles, furniture, aircraft sub-assemblies and the like. Many of those assembly operations utilize production line techniques wherein the adhesive applicator must be moved by an operator to and around the assembly part during application of the adhesive to the substrate. In such applications the adhesive is quite commonly applied to the substrate by an adhesive hand gun to which the molten adhesive is supplied through a flexible hose. In this type of system the molten feed stock or molten adhesive is converted from the solid state (e.g., pellets, bulk, or chunks) to a molten state by a melter structure such as a melting tank. The molten feed stock is then pumped from the melter structure to a gun or dispenser through a feed hose within which the molten feed stock is maintained at a temperature on the order of 350.degree. F. and a pressure of several hundred pounds per square inch. That feed hose as well as the dispenser gun or hand gun to which the hose supplies the molten feed stock are both commonly heated so as to maintain the feed stock in the molten state when the gun is not being used to dispense material, or to re-melt the feed stock if the gun is shut down for an extended period, i.e., overnight, between shifts, etc.
These feed hoses are handled and quite often come into contact with operators who are handling the dispensing guns to which the hoses are attached. Therefore, the hoses are very well insulated so as to maintain molten material on the inside of the hose at 350.degree. F. and still be only warm to the touch on the outside of the hose. In the past this hose insulation has been subject to failure and it has therefore been an objective of this invention to provide an improved hot melt adhesive dispensing hose which is not subject to insulation degradation and ultimate resulting failure of the hose.
Another problem encountered with prior hot melt adhesive dispensing hoses is the very substantial power requirements required for those hoses to maintain a preset temperature of molten adhesive within the hose. It has, therefore, been another objective of this invention to provide an improved hose which has less thermal heat loss and therefore requires less power to maintain the molten adhesive at a preset temperature within the hose.
Still another objective of this invention has been to provide an improved hose which is less expensive to manufacture than hoses which have been used in the past for transporting hot melt adhesive from a melter to a dispensing gun.